Specific -Selectivity in the Oxidative Isomerization of Allyl Ethers to Generate Geometrically Defined -Enol Ethers Using a Cobalt(II)(salen) Complex Catalyst.

Enol ether structural motifs exist in many highly oxygenated biologically active natural products and pharmaceuticals. The synthesis of the geometrically less stable -enol ethers is challenging. An efficient -selective oxidative isomerization process of allyl ethers catalyzed by a cobalt(II) (salen) complex using -fluoro-2,4,6-trimethylpyridinium trifluoromethanesulfonate (MeNFPY•OTf) as an oxidant has been developed. Thermodynamically less stable -enol ethers were prepared in excellent yields with high geometric control. This methodology also demonstrates the effectiveness in controlling the -selective isomerization reaction of diallyl ethers at room temperature. This catalytic system provides an alternative pathway to extend the traditional reductive isomerization of allyl ethers.